9727037 Holtsford Flowers exhibit a wide range of shapes, sizes, colors and scents. The diversity of floral features is thought to have evolved as a consequence of a long history of interactions with the animals that forage for pollen and nectar and in so doing, transfer pollen among flowers. Plants with flower traits that elicit favorable pollinator service should have more offspring so that favorable floral traits will increase in frequency. If different pollinators prefer different types of flowers then pollen transfer between plants with different flowers will be reduced which may lead to the evolution of new plant species. This project will experimentally address two key questions in the logical but untested scenario outlined above - what floral features affect pollinator interactions and are pollinators choosy enough to cause a divergence in floral form? Two species of wild tobaccos (Nicotiana alata and N. forgetiana, Solanaceae), provide an excellent opportunity for experimentation. These species are interfertile, morphologically divergent, and their ranges overlap in southern Brazil. Their floral morphology, color, phenology, and our observations suggest they are adapted to different pollinators (N. alata is pollinated by hawkmoths, N. forgetiana is pollinated by hummingbirds and bees). An F2 population derived from interspecific crosses shows tremendous variation in many floral traits. By sowing this hybrid population in an experimental garden within both species' natural range we will be able to determine which floral traits are most important in attracting different kinds of pollinators. Then, the offspring of these open-pollinated flowers will be grown to see whether the pollinators' behavior changed the distribution of floral traits in the next generation. This work is important because it will provide detailed information about plant-pollinator interactions and will provide an experimental test of a pro minent speciation scenario. We know very little about the formation of new species, a shortcoming that is especially important because we are losing species to extinction at an unprecedented rate.
